1. Field of the Invention
The present invention relates to apparatus and methods that are particularly, but not exclusively, suited for radially expanding tubulars in a borehole or wellbore. It will be noted that the term “borehole” will be used herein to refer also to a wellbore.
2. Description of the Related Art
It is known to use an expander device to expand at least a portion of a tubular member, such as a liner, casing or the like, to increase the inner and outer diameters of the member. Use of the term “tubular member” herein will be understood as being a reference to any of these and other variants that are capable of being radially expanded by the application of a radial expansion force, typically applied by the expander device, such as an expansion cone.
The expander device is typically pulled or pushed through the tubular member to impart a radial expansion force thereto in order to increase the inner and outer diameters of the member. Conventional expansion processes are generally referred to as “bottom-up” in that the process begins at a lower end of the tubular member and the cone is pushed or pulled upwards through the member to radially expand it. The terms “upper” and “lower” shall be used herein to refer to the orientation of a tubular member in a conventional borehole. The terms being construed accordingly where the borehole is deviated or a lateral borehole for example. “Lower” generally refers to the end of the member that is nearest the formation or pay zone.
The conventional bottom-up method has a number of disadvantages, and particularly there are problems if the expander device becomes stuck within the tubular member during the expansion process. The device can become stuck for a number of different reasons, for example due to restrictions or protrusions in the path of the device.
In addition to this, there are also problems with expanding tubular members that comprise one or more portions of member that are provided with perforations or slots (“perforated”), and one or more portions that are not provided with perforations or slots (“non-perforated”), because the force required to expand a perforated portion is substantially less than that required to expand a non-perforated portion. Thus, it is difficult to expand combinations of perforated and non-perforated tubular members using the same expander device and method.
Some methods of radial expansion use hydraulic force to propel the cone, where a fluid is pumped into the tubular member down through a conduit such as drill pipe to an area below the cone. The fluid pressure then acts on a lower surface of the cone to provide a propulsion mechanism. It will be appreciated that a portion of the liner to be expanded defines a pressure chamber that facilitates a build up of pressure below the cone to force it upwards and thus the motive power is applied not only to the cone, but also to the tubular member that is to be expanded. It is often the case that the tubular members are typically coupled together using screw threads and the pressure in the chamber can cause the threads between the portions of tubular members to fail. Additionally, the build up of pressure in the pressure chamber can cause structural failure of the member due to the pressure within it if the pressure exceeds the maximum pressure that the material of the member can withstand. If the material of the tubular bursts or the thread fails, the pressure within the pressure chamber is lost, and it is no longer possible to force the cone through the member using fluid pressure.
Also, in the case where the cone is propelled through the liner using fluid pressure, where the outer diameter of the tubular member decreases, the surface area of the cone on which the fluid pressure can act is reduced accordingly because the size of the expander device must be in proportion to the size of the tubular member to be expanded.